This invention relates to an axial piston pump or motor. For convenience of description, reference is hereinafter made to hydraulic pumps. However, it should be noted that the concept of this invention can be applied to hydraulic motors as well.
Bent axis type axial piston pumps generally comprises a casing, a shaft rotatably supported in the casing, a torque plate mounted on the shaft for simultaneous rotation therewith, a cylinder block mounted for rotation about an axis inclined to and intersecting the axis of the shaft and formed with a plurality of cylinder bores parallel with the inclined axis and open toward the torque plate, a plurality of pistons slidably inserted into the cylinder bores, with a connecting rod connecting each of the pistons to the torque plate, and a universal link for synchronizing the rotation of the cylinder block and that of the torque plate.
In the above art arrangement, provision of the connecting rod is essential to avoid swinging or vibration of the outer ends of the piston rods caused upon simultaneous rotation of the torque plate and the cylinder block. In order to increase the displacement of the cylinder, the angle of inclination of the cylinder bore is set to as large a value as possible, say, 20.degree.-40.degree. , with resulting increase in the stroke of the pistons and the amplitude of vibration of the outer ends of the piston rods. Provision of the connecting rod with the increased piston stroke makes the pump complicated in construction and large in size, particularly, in the axial dimension.
Moreover, in the prior art arrangement the rotary shaft can be supported at only one side of the casing despite relatively large radial and axial loads imposed on the shaft, so that high-grade expensive large bearings are required. This also adds to the size, weight and cost of the pump. Therefore, it is highly desirable to eliminate the connecting rod and at the same time support the shaft at the opposite sides of the casing by less expensive smaller bearings thereby to simplify the construction and reduce the size and the manufacturing and maintenance cost, while achieving a high performance.
The universal link provided in the above-mentioned prior art arrangement for synchronization of the rotation of the cylinder block and that of the torque plate is a link provided at its opposite ends with universal joints, which are connected to the centers of the cylinder block and the torque plate for synchronization of the rotation of the two members. This link also not only adds to the structural complexity of the pump but also makes it impossible to support the shaft at the opposite sides of the casing without undue increase in the size of the pump. Therefore, it is also highly desirable to provide a synchronizing mechanism which is simple in construction and ensures exact synchronization of the rotation of the cylinder block and that of the torque plate while allowing the shaft to be supported at the opposite sides of the casing.
A typical axial piston pump of the variable displacement type is provided with a port block which includes passages to supply working fluid to the cylinder bores formed in the cylinder block. The port block together with the cylinder block is inclinable so that the angle of the axis of the cylinder block with respect to the axis of rotation of the shaft can be changed. A hydraulic actuator is provided to drive the port block together with the cylinder block, and an external control valve is provided outside the casing to control the supply of working fluid to the actuator thereby to control the inclination of the port block and consequently the cylinder block. With such an external valve, however, it is impossible to effect fine and accurate control of the displacement of the pump since the position of the cylinder block cannot be accurately detected by mere operation of the external control valve.
It is therefore highly desirable to provide a device which is simple and yet enables accurate control of the angle of inclination of the port block and consequently the displacement of the pump.
In hydraulic pumps or motors, hydraulic pressure acts on the surfaces of various component parts and members, and it is necessary to avoid undue friction and rapid wear of the sliding surfaces and eliminate axial load being imposed on the shaft thereby to ensure smooth operation and high performance of the machine.
Accordingly, it is one object of the invention to provide a bent axis type axial piston pump or motor which is simple in construction, compact in size and superior in performance.
Another object of the invention is to provide such a pump or motor as mentioned above as a tandem type.
Another object of the invention is to provide such a pump or motor as mentioned above which is capable of accurately changing the inclination of the cylinder block thereby to accurately control the displacement.
Another object of the invention is to provide in such a pump or motor a mechanism for synchronizing the rotation of the torque plate and that of the cylinder block, which is simple in construction and reliable in operation.
An additional object of the invention is to provide such a pump or motor as mentioned above in which static pressure balance is established at the opposite sides of the torque plate, the opposite sides of the pistons and the opposite sides of the cylinder block thereby to prevent undue friction between the sliding surfaces and wear thereof and accomplish high performance of the machine.